The present invention relates to a method for preparing optically active pyrroloazepine derivatives useful as drugs or raw materials as well as intermediates for the synthesis of these drugs. More particularly, it relates to a method for preparing optically active pyrroloazepine derivatives by asymmetric reduction methods.
Pyrrolo[3,2-c]azepine derivatives are important compounds useful as drugs for treatment of cardiovascular disease or raw materials as well as intermediates for the synthesis of these drugs. For example, International Patent Publication Number WO97/20845 disclosed pyrroloazepine derivatives having strong serotonin-2 receptor antagonistic action of excellent selectivity. The compounds are useful, for example, for the prevention or treatment of ischemic heart diseases such as angina pectoris, arrhythmia, myocardial infarction, cardiac insufficiency and post-PTCA (Percutaneous Transluminal Coronary Angioplasty) restenosis; cerebrovascular disturbances such as cerebral infarction and cerebral sequelae after subarachnoid hemorrhage; peripheral circulatory disturbances such as arteriosclerosis obliterans, Raynaud""s disease and Buerger""s disease; and hypertension.
Further, Japanese Laid-open Patent Publication Number Hei 10-251258disclosed compounds having pyrrolo[3,2-c]azepine skeleton for treatment of cardiovascular diseases.
Among these pyrrolo[3,2-c]azepine derivatives useful for drugs, there are some compounds having asymmetric carbon atoms in their molecule. For example, several pyrrolo[3,2-c]azepine derivatives disclosed in International Patent Publication Number WO97/20845 have a hydroxyl substituent at the 8-position carbon atom and therefore, these compounds have one pair of enantiomers due to the presence of asymmetric carbon atom at the 8-position.
It is well known that in the case of the compound having one pair of enantiomers, pharmacological activities and toxicities of both enantiomers sometimes greatly differs from each other (C. C. Pfeiffer, Science, Vol. 124, 29 (1956); F. P. A. Lehmann, Quant. Struct. Act. Relat., Vol. 6, 57 (1987)). Therefore, when pharmacological activities and toxicities of optically active compounds are different from each other, it is demanded to select one optically active compound having more effectiveness and safety margin in comparison to their pharmacological activities, pharmacokinetics, side effects and toxicities, totally.
For the methods to obtain the optically active compound, it is divided broadly into two methods. That is, by mean of optical resolution method and asymmetric synthesis method for the desired optically active compound. As the former method, it is generally known a method for separating racemic compounds by using optically active column chromatography, by recrystallization of diastereoisomers which is derived by introducing the group having other asymmetric center or by reacting with other optically active acids or bases, by using enzyme reaction, and so on. However, these methods have a disadvantage that the chemical yield of the desired optically active compound is 50% at maximum.
As the later method, asymmetric synthesis is a typical method to obtain the desired optically active compound selectively. Examples of this asymmetric synthesis method are a method for synthesis of the desired optically active compound by using optically active sugars or amino acids as the starting materials and utilizing their stereo arrangement, a method for deriving to optically active compound from its precursor which is non optically active compound by introducing the group stereoselectively or by reducing stereoselectively, and so on. The chemical yield of the desired optically active compound by asymmetric synthesis is 100% theoretically and that makes this method advantageous; however, the optical yield is greatly changed by the substrate to be used and the optical and chemical yields are also greatly changed by the reaction conditions such as reagents, solvents, concentrations of substrate, and reaction temperature to be used. Therefore, there are extremely difficult to determine the reaction systems or the reaction conditions to be used for the asymmetric synthesis.
Furthermore, it is necessary to conduct the reaction at super-low temperature to obtain high optical yield of the asymmetric synthesis. The operation such as preparing a reagent is very complicated and the starting materials or reagents necessary for the production are expensive. These points are recognized to be disadvantages at the presence. That is, it is important to select the best reaction conditions for every substrate to be used in the asymmetric synthesis. Further, in the case of the asymmetric synthesis using the asymmetric catalyst, it is important to select the best asymmetric catalyst and reaction conditions suitable for the individual substrate.
For example, in the above-mentioned International Patent Publication Number WO97/20845, several synthetic methods for preparing the optically active pyrrolo[3,2-c]azepine compounds having a hydroxyl substituent at the 8-position are disclosed. Nevertheless, these methods are not sufficient for the industrial methods in operational and economical standpoints, and further improvements are required. In the Patent Publication, the methods for preparing the optically active pyrroloazepine derivatives from racemic pyrroloazepine derivatives by using optically active column chromatography, by recrystallization of salts with optically active acids, or by enzyme reaction are disclosed, and the desired optically active pyrroloazepine derivatives can be prepared by using one of these methods or the combination thereof. Although, these methods are simple methods for preparing the optically active pyrroloazepine derivatives, the chemical yield is low and it is not economically sufficient.
Further, other methods for preparing the optically active pyrroloazepine derivatives, for example, an asymmetric reduction method of ketone compounds, i.e., precursors of pyrroloazepine derivatives, using boran as reducing reagent with optically active oxazaborollidine catalyst, or using ruthenium complex catalyst for hydrogen transfer reduction, is disclosed.
However, these methods have several disadvantages, such as complication in reagents"" preparing, requirement on selecting the strict reaction conditions, high cost of reagents and low chemical yield, and are not economically sufficient.
Under these circumstances, the purpose of the present invention is to provide the methods for preparing the optically active pyrroloazepine derivatives useful for drugs in simple, economical as well as industrial applicable scale. More specifically, the present invention is to provide the simple and economical methods for preparing the optically active pyrrolo[3,2-c]azepine compounds having a hydroxyl substituent at the 8-position from their precursors, i.e., ketone compounds having carbonyl group at the 8-position, by the asymmetric reduction.
The present inventors have proceeded with extensive investigation to develop the industrial applicable methods for preparing the optically active pyrroloazepine derivatives, and it is found that the desired optically active pyrroloazepine compounds can be synthesized easily in good chemical and optical yields by combining the asymmetric reduction process of ketone compounds using metal hydride compound and alcohol compound in the presence of optically active cobalt complex catalyst, and a purification process of the resulting pyrroloazepine compound. The present invention has been completed based on the findings mentioned above.
Accordingly, as one aspect of the present invention, it is provided a method for preparing the optically active pyrroloazepine derivatives represented by the following formula (I): 
wherein Z represents optionally substituted phenyl group, which comprises;
a process for the asymmetric reduction of the ketone compound represented by the following formula (II): 
wherein Z has the same meaning mentioned above, by using metal hydride compound and alcohol compound in the presence of optically active cobalt complex catalyst, and,
a process for the purification of the resulting compound.
As another aspect of the present invention, it is provided a method for preparing the optically active pyrroloazepine derivatives represented by the following formula (I): 
wherein Z has the same meaning mentioned above, which comprises;
a process for the asymmetric reduction of the ketone compound represented by the following formula (III): 
wherein Y represents a halogen atom, by using metal hydride compound and alcohol compound in the presence of optically active cobalt complex catalyst to obtain the optically active alcohol compound represented by the following formula (IV): 
wherein Y has the same meaning mentioned above,
a process for reacting the resulting alcohol compound of the formula (IV) with the piperazine compound represented by the following formula (V) or salt thereof: 
wherein Z has the same meaning mentioned above, and,
a process for the purification of the resulting compound.
As still another aspect of the present invention, it is provided a method for preparing the optically active pyrroloazepine derivatives of the formula (I), wherein the ligand of optically active cobalt complex catalyst is one enantiomer of the following formula (VI): 
wherein this formula represents an optical active compound,
in which two mesityl groups are located in trans form to each other,
in which said enantiomer is derived from the protonated compound having levorotatory (the optical rotatory power is negative) represented by the following formula (VII). 
As still further aspect of the present invention., it is provided a method for preparing the optically active pyrroloazepine derivatives of the formula (I), wherein cobalt atom of optically active cobalt complex catalyst is divalent cobalt [Co(II)] or trivalent cobalt [Co(III)].
As still further aspect of the present invention, it is provided a method for preparing the optically active pyrroloazepine derivatives of the formula (I), wherein alcohol compound used in the reaction is tetrahydrofurfuryl alcohol.
As still another aspect of the present invention, it is provided a method for preparing the optically active pyrroloazepine derivatives of the formula (I), wherein the asymmetric reduction is conducted in solvent containing tetrahydrofuran.
The optically active pyrroloazepine derivatives represented by the formula (I) of the present invention can be prepared in accordance with the following reaction scheme.
In the reaction scheme, the groups Y and Z have the same meanings mentioned above. 
That is, the present invention is to provide following two methods for preparing the optically active pyrroloazepine derivatives of the formula (I).
Method 1
In accordance with this method 1, it is provided a method for preparing the optically active pyrroloazepine derivatives of the formula (I) comprising (a) a process of the asymmetric reduction of the ketone compound of the formula (II) with metal hydride compound and alcohol compound in the presence of optically active cobalt complex catalyst, and (b) a process for the purification of the resulting compound obtained in process (a).
The ketone compound of the formula (II) to be used in the method 1 can be obtained by the reaction of the ketone compound of the formula (III) with the piperazine compound of the formula (V) or salt thereof.
Method 2
In accordance with this method 2, it is provided a method for preparing the optically active pyrroloazepine derivatives of the formula (I) comprising (a) a process of the asymmetric reduction of the ketone compound of the formula (III) with metal hydride compound and alcohol compound in the presence of optically active cobalt complex catalyst to obtain the alcohol compound of the formula (IV), (b) a process for reacting the resulting alcohol compound of the formula (IV) with the piperazine compound represented by the formula (V) or salt thereof, and (c) a process for the purification of the resulting compound obtained in process (b).
The present invention also provides a method for preparing the optically active compounds of the formula (IV), which comprises conducting the asymmetric reduction of the ketone compound of the formula (III) with metal hydride compound and alcohol compound in the presence of optically active cobalt complex catalyst:.
Optically active cobalt complex catalyst, metal hydride compound and alcohol compound used in the asymmetric reduction of the present invention, are used of these described in Japanese Laid-open Patent Publication Number Hei 9-151143.
The present invention is described in more detail by illustrating the each method.
The method 1 of the present invention is conducted by (a) a process of the asymmetric reduction of the ketone compound of the formula (II) with metal hydride compound and alcohol compound in the presence of optically active cobalt complex catalyst, and (b) a process for the purification of the resulting compound obtained in process (a) to obtain the compound of the formula (I), represented by the following reaction scheme. 
wherein Z represents optionally substituted phenyl group.
The examples of the optionally substituted phenyl group include unsubstituted phenyl group; phenyl group substituted by halogen atom such as fluorine, chlorine and so on; phenyl group substituted by alkoxy group such as methoxy group; phenyl group substituted by hydroxyl group and its acyl derivatives; phenyl group substituted by straight or branched alkyl group; phenyl group substituted by nitro group, and the like.
The method 2 of the present invention is conducted by (a) a process of the asymmetric reduction of the ketone compound of the formula (III) with metal hydride compound and alcohol compound in the presence of optically active cobalt complex catalyst to obtain the alcohol compound of the formula (IV) as intermediate, (b) a process for reacting the resulting alcohol compound of the formula (IV) with the piperazine compound represented by the formula (V) or salt thereof, and then (c) a process for the purification of the resulting compound obtained in process (b) to obtain the compound of the formula (I). 
wherein Y represents a halogen atom and Z has the same meaning mentioned above.
The suitable halogen atom represented by xe2x80x9cYxe2x80x9d in the ketone compound of the formula (III) may include chlorine, bromine and iodine atom, and a chlorine atom is most preferable.
Although preparation of the optically active pyrroloazepine derivatives of the formula (I) of the present invention may be conducted by the above-mentioned two methods, and both methods are suitable for the production of the optically active pyrroloazepine derivatives of the formula (I), the method 2 is more preferable in view of simple operation system.
The examples of optically active cobalt complex catalyst to be used in the present invention may include optically active cobalt complex catalyst described in Japanese Laid-open Patent Publication Number Hei 9-151143. The ligands of the optically active cobalt complex catalyst may be optically active ligands described in said Patent Publication. Among them, one enantiomer divided from the following one pair of enantiomers ((S, S)-form, or (R, R)-form) represented by the following formula (VI): 
wherein this formula represents an optically active compound, in which two mesityl groups are located in trans form to each other, may be preferably used as a ligand.
This ligand, i. e., one enantiomer of the formula (VI) can be obtained from the protonated compound represented by the following formula (VII): 
wherein this formula represents an optically active compound, in which two mesityl groups are located in trans form to each other, having levorotatory [for example, optical purity of the compound (VII) is 99% e.e.; and specific rotatory power is xe2x88x92186xc2x0; [xcex1]D28xe2x88x92186xc2x0 (c=1.0 in chloroform)].
Cobalt atom of optically active cobalt complex catalyst is divalent cobalt [Co(II)] or trivalent cobalt [Co(III)]. The optically active cobalt (II) complex catalyst, in which the cobalt atom is divalent cobalt [Co(II)], is represented by the following formula (VIII). 
wherein, the compound represented by this formula or one protonated enantiomer having levorotatory (the optical rotatory power is negative) is used as the optically active ligand.
The optically active cobalt (III) complex catalyst, in which the cobalt atom is trivalent cobalt [Co(III)], is represented by the following formula (IX). 
wherein, X represents a halogen atom or an acetoxy group, the compound represented by this formula or one protonated enantiomer having levorotatory (the optical rotatory power is negative) is used as the optically active ligand.
The amount of optically active cobalt complex catalyst used in the present invention may vary in accordance with ketone compound as substrate, metal hydride compound, alcohol compound and solvent to be used. It is desirable to use optically active cobalt complex in a proportion of 0.05 to 10.0 mol %, and more preferably 0.1 to 2.0 mol % per 1 mole of the ketone compound.
The examples of metal hydride compound used in the present invention include those described in Japanese Laid-open Patent Publication Number Hei 9-151143. Among them, sodium borohydride is preferably used in view of operation system. The amount of sodium borohydride is in a proportion of 1.0 to 2.5 moles per 1 mole of the ketone compound.
The examples of alcohol compound used in the present invention may include those described in Japanese Laid-open Patent Publication Number Hei 9-151143. Among them, tetrahydrofurfuryl alcohol is preferably used. The amount of the tetrahydrofurfuryl alcohol is in a proportion of 4 to 6 moles per 1 mole of the ketone compound.
In the practice of the present invention, the reaction is preferably carried out in a liquid phase. A solvent may be used if necessary. Useful examples of the solvent are those described in Japanese Laid-open Patent Publication Number Hei 9-151143, and for example, may include halide solvent such as chloroform; aromatic solvent such as toluene; ether solvent such as tetrahydrofuran; and so on. Preferred solvent is tetrahydrofuran. The highly dehydrated solvents or commercially available solvents may also be used in this reaction. The amount of the solvent is generally 1 to 100 L per 1 mole of the ketone compound. The optically active pyrroloazepine derivatives can be obtained in high chemical and optical yields when solvent is used in the range mentioned above.
The reaction temperature of this asymmetric reduction process is generally xe2x88x92100xc2x0 C. to 50xc2x0 C., preferably xe2x88x9280xc2x0 C. to 30xc2x0 C., more preferably xe2x88x9260xc2x0 C. to 10xc2x0 C. There is an advantage that the reaction may also be carried out under simple condition such as ice cooling and still high asymmetric yield is obtained. The reaction can be carried out under normal atmospheric pressure and preferably under nitrogen or argon gas atmosphere for stability of catalyst and compound to be produced. The reaction time of the asymmetric reduction is generally 10 minutes to 5 days. Progress of the reaction can be monitored by taking samples from the reaction mixture at intervals and analyzing them by thin layer chromatography (TLC), high-performance liquid chromatography (HPLC) or the like, and the reaction may be terminated when signal of the starting material, i.e., ketone compound is disappeared.
In the method 2 of the present invention, the reaction of the alcohol compound of the formula (IV), which is obtained by the asymmetric reduction of the ketone compound (III), with the piperazine compound represented by the formula (V) or salt thereof to obtain the optically active pyrroloazepine derivatives, can be carried out in the solvent such as methanol, ethanol, dimethylformamide, dimethyl sulfoxide, acetonitrile, propionitrile, acetone, 2-butanone, tetrahydrofuran, dioxane, toluene and the like. The reaction may be carried out, if necessary, in the presence of organic base such as triethylamine, pyridine, collidine, potassium t-butoxide and the like, or inorganic base such as potassium carbonate, sodium carbonate, sodium hydrogen carbonate, sodium hydroxide, sodium hydride and the like. Further, the reaction may also be carried out, if necessary, in the presence of an alkali iodide such as potassium iodide, sodium iodide and the like.
Collection and purification of the desired optically active pyrroloazepine derivatives from the reaction mixture may be performed by the well-known conventional manner such as adsorption, extraction, recystallization, column chromatography and the like.